Re: [PATCH -tip] introduce sys_membarrier(): process-wide memorybarrier (v9)

From: Ingo Molnar
Date: Tue Mar 16 2010 - 09:14:35 EST



* Nick Piggin <npiggin@xxxxxxx> wrote:

> On Tue, Mar 16, 2010 at 08:36:35AM +0100, Ingo Molnar wrote:
> >
> > * Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
> >
> > > Unless this question is answered, Ingo's SA_RUNNING signal proposal, as
> > > appealing as it may look at a first glance, falls into the
> > > "fundamentally broken" category. [...]
> >
> > How is it different from your syscall? I.e. which lines of code make the
> > difference? We could certainly apply the (trivial) barrier change to
> > context_switch().
>
> I think it is just easy for userspace to misuse or think it does something
> that it doesn't (because of races).

That wasnt my question though. The question i asked Mathieu was to show how
SA_RUNNING is "fundamentally broken" for librcu use while sys_membarrier() is
not?

This is really what he claims above. (i preserved the quote)

It must be a misunderstanding either on my side or on his side. (Once that is
cleared we can discuss further usecases for SA_RUNNING.)

Thanks,

Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/